In order to exploit a deposit efficiently the valuable mineral contained in the rock must be exposed and separated off as completely as possible. Different degrees of comminution of the rock are required for exposure of the valuable mineral depending on the mineral grain size thereof. A rock containing minerals having a high grain size must therefore be comminuted less to expose the valuable mineral than a rock containing minerals having a smaller grain size.
The “mineral grain size” of the valuable mineral is taken here to mean not the grain size of the crystallites of this mineral but the local spatial extent of the phase of valuable mineral in the rock.
Previously the extracted rock was comminuted to a mean mineral grain size, with a first part of the rock which comprises a valuable mineral having a high grain size being comminuted to an unnecessary extent, and a second part of the rock which comprises a valuable mineral having a smaller grain size being insufficiently comminuted. The unnecessarily intensive comminution of the first part of the rock leads to an unnecessarily high consumption of energy for the comminution process. By contrast, the insufficient comminution of the second part of the rock leads to inadequate exposure, and consequently to inadequate separability of the valuable mineral, and therefore to ineffective exploitation of the deposit.
The mineral grain size and distribution of minerals in a rock were previously determined in a time-consuming manner in that rock samples are taken at various sites in a deposit and analyzed. Approximately first-sized lumps of rock are collected in deposits for this purpose and/or exploration drilling operations are carried out in a coarse grid to obtain cores which can be evaluated. These rock samples are analyzed in the laboratory with respect to their mineralogical and chemical composition. While the chemical analysis substantially determines the type and extent of the elements present, the type and extent of the minerals present and their spatial arrangement is determined in the mineralogical analysis. The rock samples are partially ground in the direction of defined spatial axes in order to determine the spatial arrangement of the minerals. The spatial arrangement and distribution of the minerals in the rock may be discerned by way of an optical analysis of the thin or ground sections, under a microscope for example. A spatially widely distributed arrangement of the minerals is associated with a low grain size of the minerals, while agglomerations of minerals at certain locations are associated with a higher mineral grain size.
Only a small amount of information may thus be provided with respect to the structure of a deposit or the spatial mineral grain size distribution of the valuable mineral in the deposit, and this information can only be provided after a considerable delay.
Deposit modeling, i.e. creation of a model of the deposit comprising the three-dimensional recording of layers of rock or rock formations having different grain sizes of the valuable mineral, is possible only to a limited extent owing to the small amount of information available. Extraction and comminution of the rock geared toward the rock that is present locally, i.e. its valuable mineral content and the grain size thereof, is therefore possible only to a limited extent.
WO 2010/000055 A1 discloses a method and a device for, in particular continuous, on-site analysis of drilling cuttings from drilling mud. A sample of the drilling cuttings which is representative of the rock formation being drilled is taken and analyzed with respect to the type of rock and the chemical composition. Drilling parameters, comprising the drilling depth, gamma radiation emissions and/or additional parameters are optionally also logged and correlated with the results of the sample analysis.